Electric fluid pump

ABSTRACT

An electric fluid pump includes a rotor including a permanent magnet, and including a radially outer peripheral surface covered by resin. An impeller faces a first axial end side of the rotor. A support shaft is disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller. A plain bearing part is configured to support the rotor and the impeller rotatably with respect to the support shaft. A first groove is formed in the radially outer peripheral surface of the rotor, and extends from the first axial end side of the rotor to a second axial end side of the rotor opposite to the first axial end side.

BACKGROUND OF THE INVENTION

The present invention relates to an electric fluid pump.

Japanese Patent Application Publication No. 2006-296125 discloses an electric fluid pump that includes a rotor and an impeller rotatably supported with respect to a support shaft disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller.

SUMMARY OF THE INVENTION

In the electric fluid pump described above, it is possible that depositing of foreign objects between the support shaft and the hole may wear the support shaft and others.

In view of the foregoing, it is desirable to provide an electric fluid pump in which a support shaft and others are suppressed from being worn.

According to one aspect of the present invention, an electric fluid pump comprises: a rotor including a permanent magnet, and including a radially outer peripheral surface covered by resin; an impeller facing a first axial end side of the rotor; a support shaft disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller; a plain bearing part configured to support the rotor and the impeller rotatably with respect to the support shaft; and a first groove formed in the radially outer peripheral surface of the rotor, and extending from the first axial end side of the rotor to a second axial end side of the rotor opposite to the first axial end side.

According to another aspect of the present invention, an electric fluid pump comprises: a rotor including a permanent magnet; an impeller facing a first axial end side of the rotor; a support shaft disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller; a plain bearing part configured to support the rotor and the impeller rotatably with respect to the support shaft; a first groove formed in a radially outer peripheral surface of the rotor, and extending from the first axial end side of the rotor to a second axial end side of the rotor opposite to the first axial end side; and a second groove formed in an axial end surface of the second axial end side of the rotor, and extending from a radially inside end side of the rotor to a radially outside end side of the rotor.

According to a further aspect of the present invention, an electric fluid pump comprises: a rotor configured to be rotationally driven by an electromagnetic force; an impeller disposed coaxially with the rotor; a support shaft disposed in a hole, and configured to support the rotor and the impeller rotatably through a plain bearing part, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller; and an outflow forcing system configured to force part of fluid by centrifugal force acting on the fluid to flow out to a second axial end side of the impeller and the rotor through a clearance between the support shaft and the hole, wherein the fluid is sucked by rotation of the impeller from a first axial end side of the impeller and the rotor opposite to the second axial end side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an electric fluid pump according to an embodiment of the present invention, taken along a plane containing a rotation axis or central axis of the electric fluid pump.

FIG. 2 is a perspective view of a rotator (an impeller, a rotor, etc.) of the electric fluid pump.

FIG. 3 is a plan view of the rotator of the electric fluid pump, showing a second axial end side of the rotator.

FIG. 4 is a schematic partial sectional view of the electric fluid pump, taken along a plane containing a rotation axis of the rotator of the electric fluid pump.

FIG. 5 is a partial sectional view of the electric fluid pump with a magnetizing yoke, taken along a plane perpendicular to a rotation axis of the rotor, with reference to a comparative example.

DETAILED DESCRIPTION OF THE INVENTION Overall Configuration

According to an embodiment of the present invention, an electric fluid pump 1 is a water pump configured to suck and discharge cooling water as a coolant or cooling medium and as working fluid. Electric fluid pump 1 is designed for cooling, and arranged in a circulating system connected to a radiator. For example, when mounted on a hybrid electric vehicle, electric fluid pump 1 supplies cooling water to an internal combustion engine, a drive electric motor, an inverter, and others. Electric fluid pump 1 is formed as a unit, including a pumping section 2, a motor section 3, a support shaft 4, and a control section 5 in a housing 6. Motor section 3 is configured as a drive section to drive the pumping section 2. Control section 5 is configured to control operation of motor section 3. Housing 6 is formed by coupling a pump cover 61, a pump body 62, and a board housing 63. FIG. 1 is a sectional view of electric fluid pump 1 taken along a plane containing a rotation axis or central axis “O” of electric fluid pump 1. FIG. 2 is a perspective view of a rotator (an impeller 20, a rotor 31, etc.) of electric fluid pump 1. The axis O is defined as an ideal rotation axis of the rotator with respect to housing 6, and also identical to a central axis of support shaft 4. The central axis or rotation axis of the rotator is represented by “P”. For ease of explanation, an x-axis is defined as extending along the axis O (or axis P). The direction from motor section 3 (or rotor 31) to pumping section 2 (or impeller 20) is defined as an x-axis positive direction. FIG. 3 is a plan view of the rotator of the electric fluid pump, showing an x-axis negative side or second axial end side of the rotator.

Pumping Section

Pumping section 2 includes impeller 20. Impeller 20 is rotatably mounted in a pumping chamber R1 in housing 6, which is defined by pump cover 61 and pump body 62. Housing 6 includes a suction port “IN” and a discharge port “OUT”, wherein suction port IN extends along the axis O and has an opening to pumping chamber R1, and discharge port OUT extends from the periphery of pumping chamber R1 in a plane perpendicular to the axis O and has an opening to the outside of pumping chamber R1. By rotation of impeller 20, cooling water is sucked through the suction port IN into pumping chamber R1, and then flows through a discharge passage radially outside of impeller 20, and is then discharged under pressure through the discharge port OUT. Electric fluid pump 1 is a centrifugal pump configured to apply pressure to the cooling water in a radial direction by centrifugal force acting on the cooling water when impeller 20 is rotating. Impeller 20 includes a plurality of blades 201, and is formed of resin, as shown in FIG. 2. Impeller 20 is arranged at a first axial end side (x-axis positive side end) of rotor 31, and substantially coaxially with rotor 31, and formed integrally with rotor 31, and faces the suction port IN in the x-axis direction. Each blade 201 is arranged to extend outward in a radial direction from axis P. For example, each blade 201 is inclined in an opposite direction to the rotational direction of impeller 20 as followed outwardly in the radial direction, so that blades 201 are arranged in a centrifugal pattern as a whole. At the x-axis positive side of impeller 20, a shroud 21 is arranged to cover half of the radially outer periphery of impeller 20, and thereby guide the flow of the cooling water. An O-ring S1 is disposed as a sealing member between pump cover 61 and pump body 62, for ensuring liquid tightness of pumping chamber R1.

Motor Section

Motor section 3 is of a revolving-field type, wherein permanent magnets 32 as a field magnet source are provided at rotor 31, and also of a DC brushless motor. Motor section 3 is of a so-called inner rotor type, including a stator 30 and a rotor 31, wherein stator 30 has a hollow-cylindrical shape, and is accommodated in a motor chamber R2 defined by pump body 62 and others, and rotor 31 is disposed radially inside of stator 30. Motor section 3 is an interior permanent magnet motor (IPM motor) in which permanent magnets 32 are embedded in rotor 31. Stator 30 includes a stator core 30 a and a plurality of coils 30 b, wherein stator core 30 a has an annular shape, and coils 30 b are wounded around stator core 30 a. When coils 30 b are energized, stator 30 causes a magnetic flux radially inside of stator core 30 a.

Rotor 31 includes a magnetic pole holding part 31 a and a shaft part 31 b. Magnetic pole holding part 31 a includes a rotor core 310 and permanent magnets 32, and forms a cylindrical part facing the radially inner peripheral surface of stator 30 with a small radial clearance. The radially outer peripheral surface of magnetic pole holding part 31 a is covered by resin, and the axial end surface (top surface) of the x-axis positive side and the axial end surface (bottom surface) of the x-axis negative side of magnetic pole holding part 31 a are also covered by resin. Inside of magnetic pole holding part 31 a, a plurality of magnetic poles are held to correspond to the coils 30 b of stator 30, wherein north poles and south poles are arranged alternately in the circumferential direction. Magnetic pole holding part 31 a is rotationally driven by magnetic interaction (i.e. a magnetic force) with stator 30. Shaft part 31 b of rotor 31 is formed of resin, and has a central axis substantially identical to the axis P similar to magnetic pole holding part 31 a. The diameter (or radial size) of the outer periphery of shaft part 31 b is slightly smaller than that of the inner periphery of rotor core 310 described below. The first axial end side of shaft part 31 b is fixed to the x-axis negative side of impeller 20, and the second axial end side of shaft part 31 b is fixed to the x-axis positive side of magnetic pole holding part 31 a. The shaft part 31 b rotates together with magnetic pole holding part 31 a as a solid unit, and thereby transmits a torque to drive rotationally the impeller 20.

Rotor 31, which is composed of magnetic pole holding part 31 a and shaft part 31 b, is formed integrally with impeller 20 by injection of resin into a mold. Alternatively, impeller 20 may be prepared separately from rotor 31, and then fixed to rotor 31. A support hole 313 is defined to extend along the axis P and has a central axis identical to the axis P, extending axially of rotor 31 and impeller 20, and through radially inside of rotor 31 and impeller 20. The radial size (or diameter) of a major part of support hole 313 is set to increase gradually as followed from the x-axis positive side to the x-axis negative side. At the x-axis positive side end of shaft part 31 b (where shaft part 31 b is connected to impeller 20), the end portion of the x-axis positive side of support hole 313 is formed with a first bearing holding part 314 which has a cylindrical shape and has a larger diameter than the x-axis positive side end of the major part of support hole 313. On the other hand, at the x-axis negative side end of shaft part 31 b, the end portion of the x-axis negative side of support hole 313 is formed with a second bearing holding part 315 which has a cylindrical shape and has a larger diameter than the x-axis negative side end of the major part of support hole 313.

A first bush 7 a as a first bearing is fixedly mounted to first bearing holding part 314. First bush 7 a includes a hollow-cylindrical body part 70 and a flange part 71, wherein the outer periphery of body part 70 is fitted with the inner periphery of first bearing holding part 314, and flange part 71 is provided at the first axial end side of body part 70 and is engaged with the x-axis positive side of impeller 20. A second bush 7 b as a second bearing is fixedly mounted to second bearing holding part 315. Second bush 7 b includes a hollow-cylindrical body part 70 and a flange part 71, wherein the outer periphery of body part 70 is fitted with the inner periphery of second bearing holding part 315, and flange part 71 is provided at the first axial end side of body part 70 and is engaged with the x-axis negative side of magnetic pole holding part 31 a of rotor 31. First and second bushes 7 a, 7 b are plain bearings (or sliding bearings) made of a kind of resin material superior in wear resistance.

Support shaft 4 is fixedly mounted to housing 6, extending through the support hole 313 of rotor 31 and impeller 20. Support shaft 4 supports rotor 31 and impeller 20 rotatably through the first and second bushes 7 a, 7 b. The radial size (or diameter) of the inner peripheral surface of each bush 7 a, 7 b is smaller than that of support hole 313, and is slightly larger than that of the outer peripheral surface of support shaft 4. Namely, there is a slight radial clearance between the inner periphery of each bush 7 a, 7 b and the outer periphery of support shaft 4, so that first and second bushes 7 a, 7 b can slide with respect to support shaft 4. First and second bushes 7 a, 7 b support the rotor 31 and impeller 20 rotatably with respect to support shaft 4. The first axial end (or x-axis positive side end) of support shaft 4 is formed with a larger-diameter part 40. The radial size (or diameter) of the major part of support shaft 4 except the larger-diameter part 40 is substantially constant in the x-axis direction. The size of the radial clearance between the inner periphery of the major part of support hole 313 and the outer periphery of the major part of support shaft 4 is set to increase gradually as followed from the x-axis positive side to the x-axis negative side.

Pump cover 61 is formed with a travel restriction part 610. Travel restriction part 610 is supported by a rib 611 and is placed at the axis O, wherein rib 611 projects from the inner periphery of the x-axis negative side of suction port IN of pump cover 61. The x-axis positive side end of support shaft 4 is fixed to travel restriction part 610 by fitting in through hole 612 of travel restriction part 610. The x-axis positive side of support shaft 4 is thus supported by housing 6. The axial end surface of the x-axis negative side of travel restriction part 610 and the flange part 71 of first bush 7 a face each other through a small clearance in the x-axis direction, wherein a washer 8 is disposed in this clearance to surround the support shaft 4. Movement of impeller 20 and rotor 31 in the x-axis positive direction is restricted by sliding contact between the flange part 71 of first bush 7 a and the washer 8. A holder part 64 is fixedly mounted to the axial end of the x-axis negative side of pump body 62. The larger-diameter part 40 of support shaft 4 is fixedly mounted to holder part 64 by fitting in a through hole 640 of holder part 64. The x-axis negative side of support shaft 4 is thus held by housing 6. Movement of rotor 31 and impeller 20 in the x-axis negative direction is restricted by sliding contact between the flange part 71 of second bush 7 b and larger-diameter part 40.

Stator Accommodation Chamber and Rotor Accommodation Chamber

The x-axis positive side of pump body 62 is formed with a separation wall part 620 which projects from the outer periphery of pump body 62 inward in the radial direction. The radially inner side of separation wall part 620 is formed with a hollow-cylindrical projection part 621 which projects toward the x-axis negative side. The x-axis positive side of the radially inner side of separation wall part 620 is formed with a recess 622 which accommodates an x-axis negative side part of the outer periphery of impeller 20. The motor chamber R2 in pump body 62 is separated by separation wall member 65 to define a stator accommodation chamber R21 and a rotor accommodation chamber R22. Separation wall member 65 has a thin hollow-cylindrical shape and is made of nonmagnetic metal. Separation wall member 65 includes an outer wall part 650, a flange part 651, a larger-diameter part 652, a flange part 653, and a smaller-diameter part 654, wherein outer wall part 650 has a hollow-cylindrical shape, and flange part 651 extends radially outward from the opening of the x-axis positive side of outer wall part 650, and larger-diameter part 652 has a hollow-cylindrical shape extending toward the x-axis positive side from the outer peripheral edge of flange part 651, and smaller-diameter part 654 has a hollow-cylindrical shape extending toward the x-axis negative side from the inner peripheral edge of flange part 653. The radial size (or diameter) of to the inner periphery of outer wall part 650 is set substantially equal to that of the inner periphery of separation wall part 620 (projection part 621) of pump body 62, so that the inner peripheral surfaces of outer wall part 650 and separation wall part 620 (projection part 621) are continuous and flush with each other.

The x-axis positive side end (flange part 651) of separation wall member 65 is disposed at the x-axis negative side end of projection part 621 of separation wall part 620 of pump body 62. The x-axis positive side end of a hollow-cylindrical part 641 of holder part 64 is disposed at the x-axis negative side end of separation wall member 65, wherein the hollow-cylindrical part 641 projects toward the x-axis positive side radially outside of through hole 640. Accordingly, stator accommodation chamber R21 is defined radially outside of separation wall member 65 by the inner peripheral surface of pump body 62 (including the x-axis negative side surface of separation wall part 620), and the radially outer peripheral surface of separation wall member 65, and the surface of the x-axis positive side of part of holder part 64 radially outside of the cylindrical part 641 (including the radially outer peripheral surface of cylindrical part 641). Stator accommodation chamber R21 has a closed annular space in which stator 30 is mounted.

On the other hand, rotor accommodation chamber R22 is defined radially inside of separation wall member 65 by the radially inner peripheral surface of separation wall part 620 (projection part 621) of pump body 62, and the radially inner peripheral surface of separation wall member 65, and the surface of the x-axis to positive side of part of holder part 64 radially inside of cylindrical part 641. Rotor 31 is rotatably mounted in rotor accommodation chamber R22. Rotor accommodation chamber R22 is an open space constantly communicating with the pumping chamber R1 at the x-axis positive side through a clearance between the x-axis negative side of the outer periphery of impeller 20 and the separation wall part 620 (recess 622) of pump body 62, and is filled with the cooling water supplied from the pumping chamber R1. Rotor accommodation chamber R22 communicates with pumping chamber R1 through a clearance between support hole 313 (and the inner peripheral surfaces of first and second bushes 7 a, 7 b) and support shaft 4.

An O-ring S2 as a sealing member is disposed between the radially outside of projection part 621 of separation wall part 620 and the radially inside of larger-diameter part 652 of separation wall member 65 in pump body 62. Moreover, an O-ring S3 as a sealing member is disposed between the radially inside of cylindrical part 641 of holder part 64 and the radially outside of smaller-diameter part 654 of separation wall member 65. Accordingly, fluid communication between the radially inside and the radially outside of separation wall member 65 is shut off. In this way, stator accommodation chamber R21 and rotor accommodation chamber R22 are liquid-tightly separated by O-rings S2 and S3, preventing the cooling water from flowing from rotor accommodation chamber R22 into stator accommodation chamber R21 (and a board accommodation chamber R3 detailed below).

Control Section

Board housing 63 is attached to pump body 62, covering an x-axis negative side opening of pump body 62, and defining therein the board accommodation chamber R3. Board accommodation chamber R3 is defined between board housing 63 and holder part 64. Control section 5 includes a board 50, capacitors, etc., wherein board 50 is a driver for supplying a drive current to motor section 3, and is accommodated in board accommodation chamber R3. An electric circuit (a CPU, transistors, etc.) is mounted on board 50, wherein these circuit components and capacitors constitute a converter system and a control circuit system. The converter system is configured to receive electric supply from a battery as a direct current power supply, and supply an alternating current to the coils 30 b of motor section 3. The control circuit system is configured to control the converter system. The x-axis negative side end surface of board housing 63 substantially parallel to board 50 is formed with a heat sink.

Configuration of Rotor

Magnetic pole holding part 31 a includes rotor core 310 that is formed in a hollow-cylindrical shape by layering a plurality of annular electromagnetic steel sheets in the direction of axis P as shown in FIGS. 1 and 5. Rotor core 310 includes a plurality of insertion holes 311 (six insertion hole 311 in this example), in each of which permanent magnet 32 is inserted and mounted. Each insertion hole 311 extends in the x-axis direction, wherein the x-axis positive side end of insertion hole 311 is closed by the x-axis positive side end portion of rotor core 310, and the x-axis negative side end of insertion hole 311 is open at the x-axis negative side end surface of rotor core 310. The openings of insertion holes 311 are arranged around the axis P, forming six edges of a hexagonal shape as viewed in the x-axis direction. Each permanent magnet 32 has a plate shape. The number of permanent magnets 32 is six in this example. Each permanent magnet 32 is inserted and mounted in insertion hole 311 of rotor core 310 before permanent magnet 32 is magnetized, and thereby embedded in magnetic pole holding part 31 a, and then magnetized by magnetizing yoke 9. This forms a plurality magnetic poles arranged in the circumferential direction.

As shown in the left side of FIG. 5, the outer periphery of rotor core 310 is formed with recesses 312 which are close to the ends of two adjacent insertion holes 311 in the circumferential direction around axis P, and extend in the axial direction of rotor 31. Each recess 312 includes a first recessed portion 312 a and a second recessed portion 312 b, wherein first recessed portion 312 a is relatively shallow and is close to the intermediate point between two adjacent insertion holes 311, and second recessed portion 312 b is relatively deeper, and is located substantially at the center of first recessed portion 312 a in the circumferential direction, and extends inward in the radial direction between two adjacent insertion holes 311. The provision of recess 312 serves to minimize the distance from the circumferential end of insertion hole 311 to the outer peripheral surface of rotor core 310 (recess 312). The number of recesses 312 is equal to that of insertion holes 311, which is six in this example.

Before rotor 31 and impeller 20 are formed integrally, a holder 33 is assembled to rotor core 310 in which permanent magnets 32 are mounted, as shown in FIG. 1. Holder 33 is a part made of resin for holding the permanent magnets 32. When a hollow-cylindrical part 33 a of holder 33 is fixed by fitting to the inner periphery of rotor core 310 from the x-axis negative side, a flange part 33 b of holder 33 covers the opening of the x-axis negative side of each insertion hole 311, and thereby prevents permanent magnet 32 from being dropped from insertion hole 311. The x-axis negative side surface of holder 33 is formed with a plurality of recesses 330 (six recesses 330 in this example) which extend radially and are arranged around axis P at substantially equal intervals. Each recess 330 is fitted with a first projection portion of the mold (or zig), thereby positioning the rotor core 310 (the assembly of permanent magnets 32 and holder 33) in the mold. This positioning allows a second projection portion of the mold to slightly enter the recess 312 formed at the outer periphery of rotor core 310, and thereby sets rotor core 310 (the assembly of permanent magnets 32 and holder 33) in the mold, wherein the second projection portion is formed in the mold and extends in the x-axis direction. Rotor 31 and impeller 20 are formed of resin integrally with each other by injection of resin into the mold under the condition described above. The flange part 33 b of holder 33 may be formed to cover partially the opening of the x-axis negative side of each insertion hole 311 (namely, making the insertion hole 311 partially opened). In this case alternative case, the resin material is supplied into each insertion hole 311 through the partial opening, so that it is unnecessary to fix permanent magnets 32 in insertion holes 311, which results in a reduction of the manufacturing cost.

The thus formed radially outer peripheral surface of rotor 31 is formed with a plurality of recesses referred to as first grooves 316 (six first grooves 316 in this example), each of which extends in the axial direction similar to recess 312 of rotor core 310, and is formed by drawing the second projection portion of the mold, as shown in FIGS. 2 and 3. The x-axis negative side surface of rotor 31 is formed with a plurality of recesses referred to as second grooves 317 (six second grooves 317 in this example), each of which extends radially similar to recess 330 of holder 33, and is formed by drawing the first projection portion of the mold. As shown in FIG. 2, each first groove 316 is formed in the radially outer peripheral surface of rotor 31 (magnetic pole holding part 31 a), and extends from the first axial end side (x-axis positive side) to the second axial end side (x-axis negative side), specifically, extends over the entire axial length of rotor 31 (magnetic pole holding part 31 a). In other words, the x-axis ends of first groove 316 are not closed as viewed in the x-axis direction, but are open at the axial ends of rotor 31 (magnetic pole holding part 31 a). As shown in FIG. 5, each first groove 316 is located between two permanent magnets 32 (insertion holes 311) adjacent to each other in the circumferential direction. The width (in the circumferential direction) and the depth (in the radial direction) of first groove 316 are set so that part of magnetizing yoke 9 that is a coil for magnetizing the permanent magnets 32 can be put in first groove 316.

As shown in FIG. 3, each second groove 317 is formed in the bottom surface of the second axial end side (x-axis negative side) of rotor 31 (magnetic pole holding part 31 a), and extends from the radially inside of rotor 31 to the radially outside of rotor 31. The radially outside end of second groove 317 (or the longitudinal end of second groove 317 at the radially outside of rotor 31) is located radially inside of the radially outer peripheral surface of rotor 31, and shifted from and has no overlap with the first grooves 316 in the circumferential direction of rotor 31 (specifically, located at a substantially intermediate position between two adjacent first grooves 316). As shown in FIG. 1, each second groove 317 extends from a location radially inside of permanent magnet 32 toward the radially outside. Specifically, each second groove 317 extends from a location slightly radially inside of rotor core 310 toward the radially outside.

Functions of Pump

The following describes functions of electric fluid pump 1. The rotor 31 of motor section 3 is rotatably mounted to support shaft 4, and is applied with a torque resulting from the magnetic flux generated by stator 30 in response to a control signal outputted by control section 5. Rotation of rotor 31 causes the impeller 20 to rotate and thereby causes pumping section 2 to operate. Rotation of impeller 20 causes fluid to be sucked from the x-axis positive side into pumping chamber R1, and causes major part of the fluid to be discharged through the discharge port OUT. In the present embodiment, it is configured so that part of the sucked fluid can smoothly flow between support shaft 4 and support hole 313. FIG. 4 is a schematic partial sectional view of electric fluid pump 1, showing flow of the part of the fluid by an arrow of a long-dashed short-dashed line. Rotor accommodation chamber R22 communicates with pumping chamber R1 through a clearance CL4 between the x-axis negative side of the outer periphery of impeller 20 and the separation wall part 620 (recess 622) of pump body 62, and is filled with the cooling water. The clearance CL1 between the support hole 313 (and the inner peripheral surfaces of first and second bushes 7 a, 7 b) and the support shaft 4 communicates with pumping chamber R1 at the x-axis positive side and rotor accommodation chamber R22 at the x-axis negative side, and is filled with the cooling water. The clearance CL2 between the x-axis negative side surface of magnetic pole holding part 31 a and the x-axis positive side surfaces of holder part 64 and flange part 653 of separation wall member 65, and the clearance CL3 between the radially outer peripheral surface of magnetic pole holding part 31 a and the radially inner peripheral surface of outer wall part 650 of separation wall member 65, constitute part of rotor accommodation chamber R22, and are filled with the cooling water.

Rotation of rotor 31 (magnetic pole holding part 31 a) causes centrifugal force to act on the cooling water in clearance CL2, and thereby causes the cooling water in clearance CL2 to be pressed toward the radially outside, and be sent to a space at the x-axis positive side of magnetic pole holding part 31 a through the clearance CL3. When the cooling water in clearance CL2 is pressed toward the radially outside (into clearance CL3), the cooling water is sucked from the clearance CL1 into clearance CL2 (the function of the centrifugal pump). Accordingly, as shown in FIG. 4, when impeller 20 (and rotor 31) is rotating, part of the fluid sucked into pumping chamber R1 from the x-axis positive side is sucked from the clearance CL1 into clearance CL2, and also sent from clearance CL2 into the space of the x-axis positive side of magnetic pole holding part 31 a through clearance CL3, and then discharged through clearance CL4 and discharge port OUT.

First and second bushes 7 a, 7 b function as plain bearings in the cooling water, so that the use environment of first and second bushes 7 a, 7 b is hard about wearing. Specifically, if a foreign object is trapped and deposited between bush 7 a, 7 b and support shaft 4, it may promote wear of first and second bushes 7 a, 7 b and/or support shaft 4. In the present embodiment, this problem is overcome by the feature that electric fluid pump 1 includes a flow forcing system for forcing the flow of part of the working fluid. This serves to prevent depositing of foreign objects in clearance CL1 (particularly, in the clearance between bush 7 a, 7 b and support shaft 4), and thereby suppress wear of first and second bushes 7 a, 7 b and support shaft 4.

Specifically, the radially outer peripheral surface of rotor 31 (magnetic pole holding part 31 a) is formed with first grooves 316 extending in the x-axis direction. First groove 316 serves to increase the flow sectional area of water flow in clearance CL3, and thereby force the cooling water to flow from clearance CL2 to clearance CL3 by centrifugal force, and force the cooling water to flow from the clearance CL1 to the clearance CL2. In this way, first grooves 316 constitute an outflow forcing system configured to force part of fluid by centrifugal force acting on the fluid to flow out to the clearance CL2 through the clearance CL1 (particularly, between the support shaft 4 and first and second bushes 7 a, 7 b). In this embodiment, first groove 316 is formed over the entire length of rotor 31 (magnetic pole holding part 31 a) in the axial direction, so that both of the x-axis ends of first groove 316 are opened. This serves to smooth the inflow of the cooling water from clearance CL2 to clearance CL3 and the outflow from clearance CL3 to the x-axis positive side of magnetic pole holding part 31 a, and thereby force the flow of the cooling water in clearance CL1. It may be configured so that first groove 316 does not extend over the entire length of magnetic pole holding part 31 a and one or both of x-axis ends of first groove 316 is closed. In the present embodiment, the radially outer peripheral surface of rotor 31 (magnetic pole holding part 31 a) is covered by resin, in which first grooves 316 are formed. This serves to produce the advantageous effects described above, while suppressing corrosion of rotor core 310 and others.

The bottom surface of the x-axis negative side of rotor 31 (magnetic pole holding part 31 a) is formed with second grooves 317 extending radially. Second groove 317 serves to increase the flow sectional area of water flow in clearance CL2, and thereby force the cooling water to flow from clearance CL1 to clearance CL2 by centrifugal force. In this way, second grooves 317 constitute the outflow forcing system as well as first grooves 316. In this embodiment, second groove 317 extends from the location radially inside of permanent magnet 32 toward the radially outside. This serves to shorten the distance from clearance CL1 to the radially inside end of second groove 317, and thereby smooth the outflow of the cooling water from clearance CL1 to clearance CL2. Specifically, second groove 317 extends from the location radially inside of rotor core 310 (in which permanent magnets 32 are embedded) toward the radially outside. This serves to shorten the distance from clearance CL1 to the radially inside end of second groove 317, and thereby enhance the function of electric fluid pump 1 described above.

It is optional that second groove 317 is not along a radial straight line passing through the axis P, but may be along a straight line extending from the radially inside to the radially outside without passing through the axis P. As viewed in the x-axis direction, the shape of second groove 317 is not limited to a straight shape but may be a curbed shape. One or both of the radial ends of second groove 317 may be opened. For example, second groove 317 may extend over the entire radial length of the bottom surface of the x-axis negative side of rotor 31 (magnetic pole holding part 31 a), so that both longitudinal ends of second groove 317 are opened.

In the present embodiment, the radially outside end of second groove 317 is located radially inside of the radially outer peripheral surface of rotor 31 (magnetic pole holding part 31 a) and shifted from first grooves 316 in the circumferential direction. Actual water flow in clearance CL2 has a component in the circumferential direction as well as a component in the radial direction passing through the axis P. Accordingly, even in the configuration where the longitudinal end of second groove 317 at the radially outside of rotor 31 is closed to the clearance CL3, the flow path from the longitudinal end of second groove 317 to the x-axis negative, side of first groove 316 is shortened, as compared to cases where the shifting from first groove 316 is not adopted. This serves to smooth the outflow of the cooling water from clearance CL2 to clearance CL3, and thereby force the flow of the cooling water in clearance CL1.

An additional groove may be provided to extend from the longitudinal end of second groove 317 at the radially outside of rotor 31 to the x-axis negative side end of first groove 316.

In the present embodiment, not only the radially outer peripheral surface of rotor 31 (magnetic pole holding part 31 a) but also the axial end surfaces of rotor 31 are covered by resin, wherein the axial end surface (bottom surface) of the x-axis negative side is formed with second grooves 317. This serves to obtain the advantageous effects described above, while reliably suppressing corrosion of rotor core 310 and permanent magnets 32. The feature that the recess formed by drawing the first projecting portion of the mold (or zig) is used as second groove 317, simultaneously provides the positioning means used for forming the rotor 31 and impeller 20, and the flow forcing means, and thereby reduces the manufacturing cost. Moreover, the feature that the recess 330 formed in holder 33 is used to form second groove 317, serves to simultaneously obtain the prevention of drop of permanent magnets 32 by holder 33 and the ease of forming by the positioning by recess 330, in addition to the advantageous effect described above.

The flow sectional area of clearance CL1 between the inner peripheral surface of the major part of support hole 313 and the major part of support shaft 4 is set to increase gradually as followed from the x-axis positive side to the x-axis negative side. This serves to force the flow of the cooling water in clearance CL1 from the x-axis positive side to the x-axis negative side.

In the case where the outer peripheral surface of rotor 31 (magnetic pole holding part 31 a) is covered by resin as in the present embodiment, it may adversely affect the efficiency of magnetizing the permanent magnets 32. FIG. 5 is a partial sectional view of electric fluid pump 1 with magnetizing yoke 9, taken along a plane perpendicular to the axial direction of rotor 31 (magnetic pole holding part 31 a), with reference to a comparative example. The left side of FIG. 5 shows the present embodiment in which rotor core 310 is formed with recesses 312 and the radially outer peripheral surface of magnetic pole holding part 31 a is formed with first grooves 316. The right side of FIG. 5 shows the comparative example in which no recess 312 and no first groove 316 is provided. The magnetic field caused by one of magnetizing yokes 9 is shown by a plurality of lines of magnetic force encompassing the magnetizing yoke 9. In the case where the radially outer peripheral surface of magnetic pole holding part 31 a is covered by resin, the distance from magnetizing yoke 9 to permanent magnet 32 is increased by the thickness of film of resin, as compared to the cases no resin film is provided. Accordingly, in the case where no first groove 316 is provided, it is possible in general that the number of the lines of magnetic force of magnetizing yoke 9 that fail to reach the permanent magnet 32 is increased to reduce the magnetizing efficiency.

In contrast, in the present embodiment, first groove 316 is provided between two adjacent permanent magnets 32 in the circumferential direction, to allow part of magnetizing yoke 9 to be placed in first groove 316. Since magnetizing is performed under the condition where part of magnetizing yoke 9 is located in first groove 316, the distance between magnetizing yoke 9 and permanent magnet 32 is shortened by the amount of entrance of magnetizing yoke 9 into first groove 316, and thereby increase the number of magnetic lines of magnetizing yoke 9 that reach the permanent magnet 32. This enhances the magnetizing efficiency. In other words, by commonality of the means for enhancing the magnetizing efficiency and the means for forcing the outflow of cooling water, it is possible to simplify the structure and thereby reduce the manufacturing cost. In view of the magnetizing operation by magnetizing yoke 9, it is preferable that first groove 316 has a straight shape extending in the x-axis direction.

If first groove 316 is formed without forming the recess 312 in rotor core 310, the thickness of the resin covering the radially outer peripheral surface of magnetic pole holding part 31 a becomes uneven between the portion where first groove 316 is formed and the remaining portion, which is disadvantageous in the efficiency of resin forming. This may also result in an increase in the radial size of magnetic pole holding part 31 a. In contrast, in the present embodiment, the feature that rotor core 310 is formed with recess 312, and first groove 316 is formed in the position corresponding to recess 312, serves to enhance the magnetizing efficiency even in the configuration where the outer peripheral surface of magnetic pole holding part 31 a is covered by resin, and also enhance the facility of forming by making the thickness of resin uniform. Even if the radially outer peripheral surface of magnetic pole holding part 31 a is not covered by resin, it is naturally possible to enhance the magnetizing efficiency by magnetizing under the condition where part of magnetizing yoke 9 is placed in recess 312 of rotor core 310. The second groove 317, which is formed in the bottom surface of the x-axis negative side of rotor 31 (magnetic pole holding part 31 a), is used as a means for positioning (as a recess to be engaged with a zig) when the magnetizing is performed. In this way, by commonality of the positioning means during magnetizing and the outflow forcing means, it is possible to reduce the manufacturing cost.

Advantageous Effects

The following summarizes the features of the present embodiment and produced advantageous effects.

<1> An electric fluid pump (1) includes: a rotor (31, magnetic pole holding part 31 a) including a permanent magnet (32), and including a radially outer peripheral surface covered by resin; an impeller (20) facing a first axial end side of the rotor (31); a support shaft (4) disposed in a hole (support hole 313), wherein the hole (313) extends axially of the rotor (31) and the impeller (20), and through radially inside of the rotor (31) and the impeller (20); a plain bearing part (first and second bushes 7 a, 7 b) configured to support the rotor (31) and the impeller (20) rotatably with respect to the support shaft (4); and a first groove (316) formed in the radially outer peripheral surface of the rotor (31), and extending from the first axial end side of the rotor (31) to a second axial end side of the rotor (31) opposite to the first axial end side. This serves to force the flow of the fluid in a clearance (CL1) between the support shaft (4) and the hole (313) by the first groove (316), and thereby prevent depositing of foreign objects between the support shaft (4) and the plain bearing part (7 a, 7 b), and suppress the support shaft (4) and others from being worn. The covering the radially outer peripheral surface of the rotor (31) by resin, serves to suppress corrosion of a rotor core (310) and others of the rotor (31).

<2> The electric fluid pump (1) further includes a second groove (317) formed in an axial end surface of the second axial end side of the rotor (31), and extending from a radially inside end side of the rotor (31) to a radially outside end side of the rotor (31). This serves to force the flow of the fluid in a clearance (CL1) between the support shaft (4) and the hole (313) by the second groove (317), and thereby prevent depositing of foreign objects between the support shaft (4) and the plain bearing part 1 c (7 a, 7 b), and suppress the support shaft (4) and others from being worn.

<3> In the electric fluid pump (1): the permanent magnet (32) is inside of the rotor (31); and the second groove (317) extends from a location inside of the permanent magnet (32) outwardly in a radial direction of the rotor (31). This serves to shorten the distance from the clearance (CL1) between the support shaft (4) and the hole (313) to the longitudinal end of the second groove (317) at the radially inside of the rotor (31), and thereby force the flow of the fluid in the clearance (CL1).

<4> In the electric fluid pump (1): the rotor (31) includes a rotor core (310) in which the permanent magnet (32) is disposed; and the second groove (317) extends from a location inside of the rotor core (310) outwardly in a radial direction of the rotor (31). This serves to shorten the distance from the clearance (CL1) between the support shaft (4) and the hole (313) to the longitudinal end of the second groove (317) at the radially inside of the rotor (31), and thereby force the flow of the fluid in the clearance (CL1).

<5> In the electric fluid pump (1), the second groove (317) includes a longitudinal end at the radially outside end side, wherein the longitudinal end is inside of the radially outer peripheral surface of the rotor (31) in a radial direction of the rotor (31), and close to a longitudinal end of the first groove (316) at the second axial end side of the rotor (31) in a circumferential direction of the rotor (31). This serves to shorten the distance from the end of the second groove (317) at the radially outside of the rotor (31) to the x-axis negative side end of the first groove (316), and thereby force the flow of the fluid in the clearance (CL1), even in the configuration where the end of the second groove (317) at the radially outside is not opened to the radially outer peripheral surface of the rotor (31).

<6> In the electric fluid pump (1): the rotor (31) includes therein the permanent magnet (32) as a first permanent magnet (32) and includes therein a second permanent magnet (32) adjacent to the first permanent magnet (32) in a circumferential direction of the rotor (31); and the first groove (316) is arranged between the first permanent magnet (32) and the second permanent magnet (32) in the circumferential direction, and configured to accommodate part of a coil for magnetizing the permanent magnets (32). This enhances the efficiency of magnetizing the permanent magnet (32).

<7> An electric fluid pump (1) includes: a rotor (31) configured to be rotationally driven by an electromagnetic force; an impeller (20) disposed coaxially with the rotor (31); a support shaft (4) disposed in a hole (support hole 313), and configured to support the rotor (31) and the impeller (20) rotatably through a plain bearing part (first and second bushes 7 a, 7 b), wherein the hole (313) extends axially of the rotor (31) and the impeller (20), and through radially inside of the rotor (31) and the impeller (20); and an outflow forcing system (first groove 316, second groove 317) configured to force part of fluid by centrifugal force acting on the fluid to flow out to a second axial end side of the impeller (20) and the rotor (31) through a clearance (CL1) between the support shaft (4) and the hole (313), wherein the fluid is sucked by rotation of the impeller (20) from a first axial end side of the impeller (20) and the rotor (31) opposite to the second axial end side. This serves to force the flow of the fluid in a clearance (CL1) between the support shaft (4) and the hole (313) by the outflow forcing system (316, 317), and thereby prevent depositing of foreign objects between the support shaft (4) and the plain bearing part (first and second bushes 7 a, 7 b), and thereby suppress the support shaft 4 and others from being worn.

<8> In the electric fluid pump (1), the electric fluid pump (1) is a water pump configured to suck and discharge water (cooling water) by rotation of the impeller (20). This water pump can produce the advantageous effects described above. The covering the radially outer peripheral surface of the rotor (31, magnetic pole holding part 31 a) by resin, serves to suppress corrosion of a rotor core (310) and others of the rotor (31) by contact with water.

MODIFICATIONS

The embodiment described above may be modified. Although the working fluid of the pump is water as cooling water as a coolant medium and the configuration described above is applied to the water pump in this embodiment, the configuration of the first groove and others may be applied to another electric fluid pump as long as the electric fluid pump includes a support shaft supporting a rotor and an impeller rotatably through plain bearings, wherein the support shaft is disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller. The coolant medium is not limited to water.

The plain bearings may be formed integrally with the rotor or the support shaft. In other words, the outer periphery of the support shaft or the inner periphery of the hole where the support shaft is disposed may be used also as a plain bearing. In this modification, it is possible to reduce the number of parts and the number of assembling operations. In the present embodiment, first and second bushes 7 a, 7 b are provided as plain bearings separated from rotor 31. This allows to select a material for first and second bushes 7 a, 7 b independently of the material of rotor 31, wherein the material of first and second bushes 7 a, 7 b may be one superior in bearing performance and wear resistance, and thereby enhance the function of first and second bushes 7 a, 7 b. First and second bushes 7 a, 7 b are not limited to the positions in the x-axis direction, the sizes, and the number in the shown example. Although first and second bushes 7 a, 7 b are fixed to rotor 31, and first and second bushes 7 a, 7 b slide with respect to the components (support shaft 4 and others) stationary to housing 6 in the present embodiment, it may be modified so that first and second bushes 7 a, 7 b is fixed to the components (support shaft 4 and others) stationary to housing 6, and rotor 31 slides with respect to first and second bushes 7 a, 7 b.

The entire contents of Japanese Patent Application 2013-050179 filed Mar. 13, 2013 are incorporated herein by reference.

Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims. 

What is claimed is:
 1. An electric fluid pump comprising: a rotor including a permanent magnet, and including a radially outer peripheral surface covered by resin; an impeller facing a first axial end side of the rotor; a support shaft disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller; a plain bearing part configured to support the rotor and the impeller rotatably with respect to the support shaft; and a first groove formed in the radially outer peripheral surface of the rotor, and extending from the first axial end side of the rotor to a second axial end side of the rotor opposite to the first axial end side.
 2. The electric fluid pump as claimed in claim 1, further comprising a second groove formed in an axial end surface of the second axial end side of the rotor, and extending from a radially inside end side of the rotor to a radially outside end side of the rotor.
 3. The electric fluid pump as claimed in claim 2, wherein: the permanent magnet is inside of the rotor; and the second groove extends from a location inside of the permanent magnet outwardly in a radial direction of the rotor.
 4. The electric fluid pump as claimed in claim 2, wherein: the rotor includes a rotor core in which the permanent magnet is disposed; and the second groove extends from a location inside of the rotor core outwardly in a radial direction of the rotor.
 5. The electric fluid pump as claimed in claim 2, wherein the second groove includes a longitudinal end at the radially outside end side, wherein the longitudinal end is inside of the radially outer peripheral surface of the rotor in a radial direction of the rotor, and close to a longitudinal end of the first groove at the second axial end side of the rotor in a circumferential direction of the rotor.
 6. The electric fluid pump as claimed in claim 1, wherein: the rotor includes therein the permanent magnet as a first permanent magnet and includes therein a second permanent magnet adjacent to the first permanent magnet in a circumferential direction of the rotor; and the first groove is arranged between the first permanent magnet and the second permanent magnet in the circumferential direction, and configured to accommodate part of a coil for magnetizing the permanent magnets.
 7. The electric fluid pump as claimed in claim 1, wherein the electric fluid pump is a water pump configured to suck and discharge water by rotation of the impeller.
 8. An electric fluid pump comprising: a rotor including a permanent magnet; an impeller facing a first axial end side of the rotor; a support shaft disposed in a hole, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller; a plain bearing part configured to support the rotor and the impeller rotatably with respect to the support shaft; a first groove formed in a radially outer peripheral surface of the rotor, and extending from the first axial end side of the rotor to a second axial end side of the rotor opposite to the first axial end side; and a second groove formed in an axial end surface of the second axial end side of the rotor, and extending from a radially inside end side of the rotor to a radially outside end side of the rotor.
 9. The electric fluid pump as claimed in claim 8, wherein: the permanent magnet is inside of the rotor; and the second groove extends from a location inside of the permanent magnet outwardly in a radial direction of the rotor.
 10. The electric fluid pump as claimed in claim 8, wherein: the rotor includes a rotor core in which the permanent magnet is disposed; and the second groove extends from a location inside of the rotor core outwardly in a radial direction of the rotor.
 11. The electric fluid pump as claimed in claim 8, wherein the second groove includes a longitudinal end at the radially outside end side, wherein the longitudinal end is inside of the radially outer peripheral surface of the rotor in a radial direction of the rotor, and close to a longitudinal end of the first groove at the second axial end side of the rotor in a circumferential direction of the rotor.
 12. The electric fluid pump as claimed in claim 8, wherein: the rotor includes therein the permanent magnet as a first permanent magnet and includes therein a second permanent magnet adjacent to the first permanent magnet in a circumferential direction of the rotor; and the first groove is arranged between the first permanent magnet and the second permanent magnet in the circumferential direction, and configured to accommodate part of a coil for magnetizing the permanent magnets.
 13. The electric fluid pump as claimed in claim 8, wherein the electric fluid pump is a water pump configured to suck and discharge water by rotation of the impeller.
 14. An electric fluid pump comprising: a rotor configured to be rotationally driven by an electromagnetic force; an impeller disposed coaxially with the rotor; a support shaft disposed in a hole, and configured to support the rotor and the impeller rotatably through a plain bearing part, wherein the hole extends axially of the rotor and the impeller, and through radially inside of the rotor and the impeller; and an outflow forcing system configured to force part of fluid by centrifugal force acting on the fluid to flow out to a second axial end side of the impeller and the rotor through a clearance between the support shaft and the hole, wherein the fluid is sucked by rotation of the impeller from a first axial end side of the impeller and the rotor opposite to the second axial end side.
 15. The electric fluid pump as claimed in claim 14, wherein the electric fluid pump is a water pump configured to suck and discharge water by rotation of the impeller. 